The present invention relates to gas-feed ceramic structures, such as shower plates, for use in semiconductor-producing apparatuses.
In order to feed a processing gas to the semiconductor wafer, a so-called shower plate is used. With increase in the high frequency electric power and in plasma density, it is important to uniformly feed the processing gas in a space above the semiconductor wafer. If the gas-feeding state is macro-scopically or microscopically non-uniform, arching or glow discharging occurs between parallel planar electrodes in generating plasma between the electrodes. Consequently, dielectric breakdown is likely to occur in the processing gas.
Further, it is known that arching is likely to occur in feeding the processing gas into the space above the surface of the semiconductor wafer through the shower plate. It is said that reduction in diameter of holes of the shower plate is effective to prevent the arching. For this purpose, it is known that the shower plate is provided with gas feed holes each having a diameter of 0.5 mm and a length of 10 mm.
However, it is difficult to prevent the arching by thinning the gas feed holes like this. For example, it is thought effective to reduce the diameter of the gas feed hole to not more than 0.1 mm so as to particularly effectively prevent the arching. Nevertheless, it is practically impossible to form gas feed holes, for example, having a diameter of 0.1 mm over a length of 10 mm in the ceramic shower plate.
Although not difficult to form such gas feed holes in a diameter of around 0.5 mm over a length of 10 mm in the ceramic shower plate, steps are likely to be formed on the inner wall surfaces of the gas feed holes, which readily results in turbulence. It is not practical from the working time period and from cost performance to form a sufficiently great number of such gas feed holes as having a relatively small diameter in the shower plate. Owing to this, the distance between the adjacent gas feed holes in the shower plate tends to be lower, so that the blow-out pressure through the gas feed holes becomes high. Such causes are likely to produce turbulence or swirling of the gas in the space above the semiconductor wafer. For this reason, it is difficult to effectively prevent the arching by decreasing the diameter of the gas feed holes.
It is an object of the present invention to provide a gas feed ceramic structure for feeding a gas into a semiconductor-producing apparatus, in which the gas feed structure can stabilize the gas-fed state over a wide range, prevent the gas from non-uniformly flowing and thereby suppress the arching.
The gas feed ceramic structure for feeding a gas into a semiconductor-producing apparatus according to the present invention, comprising a planar substrate having a gas-feeding surface and a rear surface, the planar substrate comprising depressions formed from the rear surface toward the gas-feeding surface to define thin portions between the depressions and the gas-feed surface, each of the thin portions comprising a plurality of gas feed holes for feeding the gas to a side of the gas-feeding surface of th e substrate, one open end of the gas feed holes being provided at the gas-feeding surface of the substrate and the other facing the depressions.
These and other objects, features and advantages of the invention will be appreciated upon reading the following description of the invention when taken in conjunction with the attached drawings, with the understanding that some modifications, variation and changes of the same could be made by the skilled person in the art to which the invention pertains.